Bi-specific antibodies are capable of binding to two different epitopes. The epitopes can be on the same antigen, or each epitope can be on a different antigen. This feature of bi-specific antibodies makes them an attractive tool for various therapeutic applications where there is a therapeutic benefit to targeting or recruiting more than one molecule in the treatment of disease. One of the approaches to form bi-specific antibody would involve concomitant expression of two unique antibody heavy chains and two unique antibody light chains. Correctly forming bi-specific antibodies in a format that is similar to wild-type remains a challenge, since antibody heavy chains have evolved to bind antibody light chains in a relatively promiscuous manner. As a result of this promiscuous pairing, concomitant expression of two antibody heavy chains and two antibody light chains naturally leads to a scrambling of heavy chain-light chain pairings. This mispairing remains a major challenge for the generation of bi-specific therapeutics, where homogeneous pairing is an essential requirement for good manufacturability and biological efficacy.
Several approaches have been described to prepare bi-specific antibodies in which specific antibody light chains or fragment pair with specific antibody heavy chains or fragments. A review of various approaches to address this problem can be found in Klein et al., (2012) mAbs 4:6, 1-11. International Patent Application No. PCT/EP2011/056388 (WO 2011/131746) describes an in vitro method for generating a heterodimeric protein in which asymmetrical mutations are introduced into the CH3 regions of two monospecific starting proteins in order to drive directional “Fab-arm” or “half-molecule” exchange between two monospecific IgG4- or IgG4-like antibodies upon incubation under reducing conditions.
Schaefer et al. (Roche Diagnostics GmbH), describe a method to assemble two heavy and two light chains, derived from two existing antibodies, into human bivalent bi-specific IgG antibodies without use of artificial linkers (PNAS (2011) 108(27): 11187-11192). The method involves exchanging heavy chain and light chain domains within the antigen-binding fragment (Fab) of one half of the bi-specific antibody.
Strop et al. (Rinat-Pfizer Inc.), describe a method of producing stable bi-specific antibodies by expressing and purifying two antibodies of interest separately, and then mixing them together under specified redox conditions (J. Mol. Biol. (2012) 420:204-19).
Zhu et al. (Genentech) have engineered mutations in the VL/VH interface of a diabody construct consisting of variant domain antibody fragments completely devoid of constant domains, and generated a heterodimeric diabody (Protein Science (1997) 6:781-788). Similarly, Igawa et al. (Chugai) have also engineered mutations in the VL/VH interface of a single-chain diabody to promote selective expression and inhibit conformational isomerization of the diabody (Protein Engineering, Design & Selection (2010) 23:667-677).
US Patent Publication No. 2009/0182127 (Novo Nordisk, Inc.) describes the generation of bi-specific antibodies by modifying amino acid residues at the Fc interface and at the CH1:CL interface of light-heavy chain pairs that reduce the ability of the light chain of one pair to interact with the heavy chain of the other pair.